Experimental Study On Permeability Of Porous Asphalt Concert

Porous asphalt concert?PAC?,an asphalt mixture technology,wa s introduced to our country in the late 1980s and has become one of types of asphalt mixture by related studies and appliances.Permeable asphalt pavement has numerous advantages,such as improving traffic safety,improving driving comfort,reducing traffic congestion,and so on.It also has a positive role in the construction of"sponge city".At present,as for permeable asphalt mixtures,most studies are focused on indoor permeability coefficient,but permeability of permeable pavement is rarely studied.Only by accurately judging the seepage performance can permeability of pavement be characterized.This thesis studies permeability coefficient and permeability coefficient of PAC-13 pervious mixture by variable head test and related test equipment is developed accordingly.The results are as follows:?1?It is the optimal embedded skeleton structure when the proportion of coarse aggregate is 51:34:15,which is confirmed by dry ramming test.The gradation of fine aggregate is designed by orthogonal test of four factors and three levels.The optimum level is A₁B₁C₂D₁,and the gradation composition of PAC-13 is determined.The performance tests are conducted on Marshall specimen of permeable mixture,and the gradation of five types of PAC-13 porosities is established.?2?This thesis explains basic theory of permeability of porous matrix,and judges the condition of flowing water in asphalt mixture based on Ergun model,and builds the model by relationship between porosity and permeability coefficient determined by Carman-Kozeny equation.Based on the classification of the pores in PAC-13 matrix,it is concluded that the porosity is the key factor affecting the permeability of this material.Besides,a new detective method is developed to make up shortcoming of previous method that the measured value of effective porosity too large.?3?According to the test of the variable water head of the indoor PAC-13permeable asphalt mixture,a test device was designed to make use of the demoulding Marshall test.The test device transforms rigid rigid contact between the previous specimen and the die into rigid flexible contact,which effectively ensures the stability and reliability of the test data.?4?A device conducted by Marshall test specimen is designed,and can be carried out in variable head test.By analyzing and judging the test data,the reasonable height of water head is 7.5cm²7.5cm.The Ergun formula is used to judge the laminar flow.It is concluded when the height of the water head is below 27.5cm,distribution of grading meets Re'<10,which satisfies Darcy's law.Through regression analysis,it can be concluded that when the permeability coefficient is greater than 1646ml/min and the permeability coefficient is greater than 0.1cm/s,the PAC-13 permeable mixture has pervious capacity.?5?A new type of water permeation instrument with a confining pressure device is designed.The continuous flow in the confining pressure device ensures the surrounding pressure state around the seepage instrument,making the three-dimensional state of the flow change to one-dimensional flow,and the accuracy of the coefficient of seepage coefficient has increased by about 3%.Through calculation,the coefficient of PAC-13permeability between the rutting plate test and the regression equation of the variable head test is between 4%⁶%,which proves the high reliability of the regression equation.It shows that the standard value of the determined seepage coefficient has certain practical significance.?6?It is found that the new water permeability meter has numerous advantages,such as large amount of water,accurate timing time and accurate switch control,and is superior to the current water permeability instrument in the determination of water permeability coefficient.